Alcoholic beverages, including beer, generally present a hostile environment for bacterial growth since such beverages tend to be relatively acidic as well as containing hop acids and carbon dioxide. There exist species of bacteria, however, that are known to be capable of surviving and causing spoilage of beer. For example, lactic acid bacteria is capable of growing in wort and causing spoilage of beer.
Prior to beer fermentation, the yeast is harvested and washed with acid to decontaminate the yeast of lactic acid bacteria. Certain strains of lactobacilli and pediococci may survive the yeast decontamination process. Additionally, these organisms may enter the beer via other ingredients of the ferment. The survival and growth of these bacteria in beer results in appreciable flavor deterioration. To avoid the expense of, and public relation problems associated with, product recalls due to spoilage, the beer must be stabilized against the development of bacteria, including these hardy strains.
Nisin is a peptide-like antibacterial substance produced by microorganisms such as Lactococcus lactis subsp. lactis (formerly known as Streptococcus lactis). Its structure is illustrated in U.S. Pat. No. 5,527,505 to Yamauchi et al. The highest activity preparations of nisin contain about 40 million IU per gram. A commercial preparation, NISAPLIN™, containing about 1 million IU per gram is available from Aplin & Barrett Ltd., Trowbridge, England. Nisin has no known toxic effects in humans. It is widely used in a variety of prepared dairy foods. Experimental use in preserving other foods has also been reported.
A number of efforts have been reported since 1975 directed to reducing uncoupled acid production in dairy fermentations by controlling the post-fermentation acidification of yogurt. In some of these studies, a nisin producing culture was introduced in an attempt to inhibit these effects. Kalra et al. (Indian Journal of Dairy Science, 28: 71–72 (1975)) incorporated the nisin producing culture Streptococcus lactis (now known as L. lactis subsp. lactis) along with the yogurt culture before fermentation. Others introduced nisin in milk prior to fermentation (Bayoumi, Chem. Mikrobiol. Technol. Lebensm., 13:65–69 (1991)) or following fermentation (Gupta et al., Cultured Dairy Products Journal, 23: 17–18 (1988); Gupta et al., Cultured Dairy Products Journal, 23: 9–10 (1989)). In all cases, the rate of post-fermentation acidification was only partially inhibited by these treatments and the yogurt continued to become more acidic throughout its shelf life.
In U.S. Pat. No. 5,527,505, yogurt was produced from raw milk by incorporating a nisin-producing strain, Lactococcus lactis subsp. lactis, along with the traditional yogurt culture consisting of Streptococcus salivarius subsp. thermophilus (ST) and Lactobacillus delbrueckii subsp. bulgaricus (LB). This patent teaches that the lactococci are needed to secrete nisin which retards the activity of ST and LB. The resulting yogurt therefore contains the lactococci used to produce the nisin. Nonetheless, the acidity of yogurt containing the nisin-producing bacteria increased by 64 to 96 percent in 14 days in various experiments inoculated with differing amounts of L. lactis subsp. lactis, compared to the initial acidity at the completion of fermentation. Other studies (Hogarty et al., J. Fd. Prot., 45:1208–1211 (1982); Sadovski et al., XX International Dairy Congress, Vol. E: 542-5–44 (1978)) also noted acid production and development of bitterness at low temperature by some mesophilic starter lactococci in dairy products.
In U.S. Pat. No. 5,015,487, the use of nisin (representative of the class of lanthionine bacteriocins) to control undesirable microorganisms in heat processed meats is disclosed. In tests involving dipping frankfurters in nisin solutions, the growth of L. monocytogenes was effectively inhibited upon storage at 4° C.
Chung et al. (Appl. Envir. Microbiol., 55, 1329–1333 (1989)) report that nisin has an inhibitory effect on gram-positive bacteria, such as L. monocytogenes, Staphylococcus aureus, and Streptococcus lactis, but has no such effect on gram-negative bacteria such as Serratia marcescens, Salmonella typhimurium, and Pseudomonas aeruginosa when these microorganisms are attached to meat.
Nisin has been added to cheese spreads and other processed foods to inhibit toxin production by Clostridium botulinum (U.S. Pat. No. 4,597,972). This patent discloses a detailed example in which chicken frankfurter components are shown to require the presence of both added nitrite and added nisin in order to prevent or delay botulinum toxin production when challenged with C. botulinum. 
Nisaplin™ has been found to preserve salad dressings from microbiological contamination, such as by Lactobacillus brevis subsp. lindneri, for an extended shelf life period (Muriana et al., J. Food Protection, 58:1109–1113 (1995)).
More recently, whey from nisin-producing cultures has been used to preserve and stabilize food compositions, including fermented dairy products, mayonnaise-type spreads, cream cheese products, meat compositions, and meat/vegetable compositions. These uses of whey from nisin-producing cultures are described in patents and/or applications entitled “Stabilization of Fermented Dairy Compositions Using Whey from Nisin-Producing Cultures”, U.S. Pat. No. 6,136,351 (Oct. 24, 2000); “Stabilization of Mayonnaise Spreads Using Whey from Nisin-Producing Cultures”, U.S. Pat. No. 6,113,954 (Sep. 5, 2000); “Stabilization of Cream Cheese Compositions Using Nisin-Producing Cultures”, U.S. Pat. No. 6,110,509 (Aug. 29, 2000); and “Stabilization of Cooked Meat Compositions Using Whey From Nisin-Producing Cultures”, U.S. patent application Ser. No. 09/386,793, filed Aug. 31, 1999. These patents and/or applications, which are owned by the same assignee as the present invention, are incorporated by reference in their entireties.
Nisin also has been used as an antimicrobial substance in beer. In European patent application EP 0 186 498, Tubb et al. disclose use of nisin to control beer spoilage. Nisin or a nisin-producing culture is added during the brewing process to control the growth of spoilage bacteria. Tubb et al. disclose adding nisin in amounts between 10 and 100 IU per milliliter. Certain strains of pediococci, such as Fulton, however, have been found to be resistant to levels of nisin as high as 200 IU of nisin per milliliter. Thus, the teachings of Tubb et al. is ineffective for preventing spoilage of beer by these resistant strains.
There remains a need for compositions and procedures related to alcoholic beverages to enhance stabilization of such beverages. In particular, there is a need for compositions and methods that will inhibit the growth of bacteria that may cause spoilage of alcoholic beverages. Such compositions and methods should be capable of inhibiting the growth of all spoilage bacteria, particularly the more resistant strains of bacteria that may otherwise survive conventional treatment methods. The present invention addresses these needs.